Process for converting high boiling point oils



April 2, 1935. R. E. WILSON 1,996,091

' PROCESS FOR CONVERTING HIGH BOILING POINT OILS Qriginal Filedno-j. 1,1926 Patented Apr. 2 1935 Fl CE PROCESS FOR of Indiana CONVERTING HIGHBOILING POINT OILS Robert E. Wilson, Chicago, n1., assignor a StandardOil Company, Whiting, Ind., a corporation Application November 1, 1926,Serial No. 145,515

Renewed January 8, 1932 10 Claims.

The present invention relates to improvements in processes for effectingthe conversion of higher boiling point distillate oils, such as naphthabottoms, gas oil and heavier distillates, if desired, into lower boilingpoint hydrocarbon ing points. following description, illustrated by theaccompanying drawing, in which apparatus capable of carrying out thepresent invention is shown diagrammatically in section.

The drawing shows a sectional view through a furnace and illustratesdiagrammatically the arrangement of the tubes through which the oil tobe converted is forced in carrying out a process exemplifying thepresent invention. In the lower portion of the furnace'setting 5 thereis provided one or more'combustion chambers 6, to which fuel is suppliedby burners I and in which combustion takes place. The walls 8 of thecombustion chamber are constructed of a suitable refractory materialcapable of withstanding the direct heat of the flame; for example, theymay be constructed of carborundum or other similar material. Combustiontakes place substantially completely within the combustion chambers 6and the combustion gases pass therefrom into a large flue 9 in the rearof the furnace by which they are conducted to the upper portion of thefurnace as hereinafter set forth. A vertical wall or partition Illseparates a compartment above the combustion chamber 6 from the flue 9which receives the combustion gases, and this compartment, indicated bythe numeral 1 I, is closed at its top by the partition l2 of fire brickor other suitable refractory material, such as a suitable chromium-ironalloy. The compartment II is exposed to the radiant surface of the walls8 of the combustion chambers 6 and is heated substantially entirely byradiant heat therefrom, although if desired, it may be in part heated bycombustion gases. The portion of the setting above the compartment llmay be divided into two passes, as by partial partition I; of suitablerefractory material. Of these the lower pass is indicated by the numerall4 and the upper pass by the numeral I5. The combustion gases from thecombustion chamber 6, pass upwardly through the vertical flue 9 and thentraverse successively the flues l4 and I5, finally reaching the stackl6.

The tubes which receive the oil to be cen verted are mounted within thefurnace and are designated individually by the numeral l1. These tubesare connected in series in sections and the pass of the oil therethroughis as follows:

The oil enters the furnace through the inlet pipe l8 and first traversesthe economizer section in the pass l5 nearest the stack travelling incountercurrent to the flow of combustion gases.

oils, for example, of the gasoline range of boi1- It will be fullyunderstood from ,the'

This section extends from broken line A to broken line B in the formshown in the drawing. From this section the oil passes through line l9(suitably a thermally insulated linepassing outside of the furnace) tothe screen section of pipes in the pass I 4 first reached by thecombustion gases. This pass extends from C to D and through this passthe oil flows concurrently with the flow of the combustion gases. Fromthe last pipe of this section, at the point D, the oil'flows through theline 20 to the lower of the rows of pipes located in the compartment ll,heated by. radiant heat from the walls ofthe combustion chamber 6. Theoil then travels in series through the pipes of this radiant'section,first traversing the row of pipes nearest the combustion chamber andthen in succession the more remote rows of pipes in the compartment ll,finally making its exit from the last pipe of the" uppermost row ed tothe heating action of radiant heat alone and finally again subjected tothe heating action of the combustion gases. While the furnace is apreferred type of furnace for carrying out the present invention and theflow of the oil relative to the heating elements as hereinbefore setforth has likewise been found highly desirable, the invention is notlimited either to the structure or the particular method of operationshown, as will be more fully hereinafter pointed out. The particularmeans herein set forth has the advantage that it is readily adaptable tothe control of operation which constitutes the present invention.

In operating conversion processes under pressure, it has hitherto beenfound that the extent of conversion taking place in the coils must becarefully limited to 5, 10 or at most 12 to 13% as a maximum in order toprevent rapid choking of the coils by coking and consequent shut-downtherein at least under critical temperatures, will permit the formationof vapor but will maintain the mixture of vapor and unvaporized liquidin the form of a foam in which the vaporized portion is maintained asdiscontinuous bubbles and 'yet not permit vaporization to the extentthat the unvaporized stock carried along as'drops or a film in a vapormedium. For example, with a charging stock passing through the coil ofthe nature of gas oil, and with a maximum tempera ture attained of about915 F., a minimum pressure of 1100 lbs. per square inch must bemaintained. With variations in the maximum temperature attained, theremay be corresponding variations in the pressure required; thus, as anapproximate rule, it may be stated that a variation of 15 F. 'intemperature attained in either direction requires a correspondingvariation in the minimum pressure required of about 100 lbs. on the oil.Similarly, variations in the charging stock necessitate variations inthe corresponding temperature and pressure conditions. Thus, with acharging stock of the nature of naphtha bottoms, a minimum pressure of1100 lbs. per square inch is required where the maximum temperatureattained by the oil'is about 880 F. With this as a guide the requiredtemperature pressure correlation may readily be determined for eachcharging stock by a short period of observation.

JIn conjunction with the required pressure and temperature conditions ashereinbefore set forth,

"in accordance with my invention there should be a minimum velocity ofthe oil flowing through the tubes of at least 60 lbs., and preferably ofabout 80 to 90 lbs. of oil per square inch of tube cross section perminute; and withthis, the heat must be so applied that the metal wall ofthe tubes (while clean) through which the oil flows is at no point morethan 20 F., and preferably not more than F. above the maximumtemperature to which the stream of oil is heated. By operating in thismanner, the most rapid application of heat occurs while the oil is at atemperature below about 750 F., and the'rate of applicationjof heatdecreases as the temperature of the oil increases. Thus, in

the type of furnace shown, after the oil leaves the preheating sectionextending from A to B, it enters the highly heated section in pass I 4extending from C to D. The oil is still relatively cool at this time,being substantially below 750 F. and heat is therefore imparted to it ata veryrapid rate while the relatively cool oil prevents excessive to Bin pass I5, through which it flows concurrently with the combustiongases, so that the temperatures of the oil and the combustion gasesheating it gradually converge and the rate of application of heat to theoil therefore gradually dc- 1,99e,oo1

creases. By operatingin this manner, the conditions required by thisinvention, that the metal walls of the tubes (while clean) through whichthe oil flows be at no point more than 20 F. above the maximumtemperature to which the stream of oil is heated, may be maintained.This speciflvention are preferably conducted upon oils which .1

may be designated as clean cracking stocks; that is distillate oils themaximum boiling point of which in an Engler distillation at atmosphericpressure is not above 750 F. As set forth, above, ,the particularcorrelation of temperature and pressure is determined by the precisenature of the oil undergoing treatment. By operating upon such an oil inthe manner above set forth,

12 to 20% gasoline or even higher may be pro-- duced from the oil in asingle pass without refluxing and without extensive coke formation, theoil preferably being initially preheated to say 400 to 500 F. by vaporheat exchange or by other suitablemeans. The other oils not regardedas-clean cracking stocks may be operated on advantageously in accordancewith the present invention, as the extent of conversion and/or length ofrun may be. greatly increased by its use.

If desired, the products of conversion leaving the coil after beingtreated in accordance with the invention, may be retained at crackingtemperature and pressure in an enlarged chamber for further conversion.

I claim: 1

1. The method of pipe still conversion of hydrocarbon oils underpressure which comprises flowing a distillate oil heavier than gasolinethrough a. metallicly confined passage heated to cracking temperaturesexceeding 850 F., re-

so'that the maximum temperature attained by the metallic walls of theconfined passage is not more than 20 F. higher than the maximumtemperature attained by the oil.

2. The method of pipe still conversion of hydrocarbon oils underpressure which comprises flowing a distillate oil heavier than gasolinethrough a metallicly confined passage heated to cracking temperature,maintaining a velocity of flow of the oil through the passage of atleast 60 lbs. per square inch of tube cross section per minute,maintaining a pressure upon the oil in the passage such that, at itsmaximum temperature, it provides a continuous flowing liquid stream inwhich vapor is present? as discontinuous bubbles, and applying heat tothe metallic walls of the passage at a maximum temperature not more than20 F. above the maximum temperature of the oil.

3. The method of pipe still conversion of hydrocarbon oils underpressure which comprises flowing a distillate gas oil through ametallicly confined passage under pressure, the temperature attained bythe oil and the minimum pres- 'attained by the oil.

4. The method of pipe still conversion of hydrocarbon oils underpressure which comprises flowing a distillate gas oil through ametallicly confined passage under pressure, the temperature attained bythe oil and the minimum pressure thereupon being so correlated that witha maximum temperature of about 915 F. the pressure is at least 1100 lbs.per square inch and with every 15 deviation from said temperature, acorresponding deviation of lbs. in minimum pressure is permitted,maintaining a veloc-' 'ity of flow of the oil through the passage of atleast 60 lbs. per minute per square inch of cross sectional area,retaining the oil within the heated passage until a conversion intogasoline boiling point fractions exceeding 12% of the oil introduced hasbeen effected, and controlling the application of heat so that themaximum wall temperature attained by said passage is not over 20 F.above the maximum temperature attained by the oil.

5. The method of pipe still conversion of hydrocarbon oils underpressure wherein an oil heavier than gasoline is forced to flow througha confined passage in a furnace, applying heat to said confined passageto bring the oil to a temperature in excess of 850 F. in successivestages while maintaining the walls of the passageway at a temperatureabove the temperature of the contacting oil and not more than 20 F.above the maximum temperature attained by the oil, said-confinedpassageway and flowing 011 being heated by convection from hotcombTi'stion gases in an early stage of the flow, by radiant heat fromthe combustion chamber of the furnace in an intermediate stage of theflow, and in a later stage of the flow by convection from combustiongases cooled and previously used in heating the confined passageway insaid early stage, and maintaining superatmospheric pressure upon the oilwithin the passageway.

6. The method of pipe still conversion of hydrocarbon oils underpressure inwhich an oil heavier than gasoline is caused to flow througha confined passage and heat is applied to said confined passage to bringthe oil to a temperature in excess of 850 F. while maintaining the wallsof the passageway at a temperature above the temperature of thecontacting oil and not more than 20 F. above the maximum temperatureattained by the oil while the oil is flowing in said confined passagethrough a furnace in successive stages, the confined passage with theflowing oil therein being heated by convection from hot combustion gasesin said furnace in an early stage of its flow, and subsequently, in alater stage of its flow, by convection with said combustion gasestraveling concurrently with the flow of oil through the passageway,after said gases have" been used and cooled in said early stage of flow,and maintaining a superatmospheric pressure upon the oil within thepassageway.

7. The method of converting hydrocarbon oils which comprises introducingoil heavier than gasoline at a temperature below 750 F. into acontinuous confined passageway, applying heat to said confinedpassageway to bring the oil passing therethrough to a, temperature inexcess of 850 F. while maintaining the walls of the confined passagewayat a temperature above the temperature of the contacting oil and at nopoint more than 20 F. above the maximum temperature attained by the oilpassing through the passageway and retaining the oil in the confinedpassageway until a conversion into lower boiling oils exceeding 12% ofthe oil introduced has been effected.

8. In the cracking of hydrocarbon oils, the method of heating whichcomprises passing a restricted stream of the oil at a high rate ofvelocity through a radiant heat zone of a furnace and heating the sametherein to the desired maximum cracking temperature substantiallyentirely by radiant heat, thence passing the oil stream through aconvection zone of the furnace, passing combustion gases from theradiant heat zone into the convection zone as a source of heat for thelatter, and altering the heating characteristics of the combustion gasesin transit from the radiant heat zone to the convection 'zone and priorto their use in the heating of oil in the convection zone to maintainthe oil at said desired maximum temperature in the convection zone whileavoiding any substantial increase in such maximum temperature.

9. In the crackingv of hydrocarbon oils, the method of heating whichcomprises passing a restricted stream of the oil at a high rate ofvelocity through a radiant heat zone of a furnace substantially withoutthe main streamof combustion gases and heating the same therein to thedesired maximum cracking temperature preponderantly by radiant heat,thence passing the oil stream through a convection zone of the furnace,passing combustion gases from the radiant heat zone into the convectionzone'as a source of heat for the latter, and altering the heatingcharacteristics of the combustion gases in transit from the radiant heatzone to the convection zone and prior to their use in the heating of oilin the convection zone to maintain the oil at cracking temperature tothereby effect soaking thereof.

10. In the crackingof hydrocarbon oils, the method of heating whichcomprises passing a restricted stream of the oil at a high rate ofvelocity through a radiant heat zone of a furnace substantially withoutthe main stream of gases and heating the same therein to the desiredmaximum cracking temperature preponderantly by radiant heat, thencepassing the oil stream through a convection zone of the furnace, passingcombustion gases from the radiant heat zone into the convection zone asa source of heat for

